Note: Descriptions are shown in the official language in which they were submitted.
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COATING SYSTEM
10 1. Field:
Inventive subject matter described herein relates to a Coating System for
providing medical device surfaces, or parts thereof, with a variety of desired
performance characteristics which include, but are not limited to, a group of
materials that provide for radiopacification, lubricity, elution of a
secondary
compound such as a drug, echogenic properties, thermal or electrically
insulative
properties or chemical indicators.
Inventive subject matter employs a Binder material, solvent(s) to thin the
Binder if need be and an active agent or agents which can then be applied to
various Medical Device surfaces to provide a novel coating which possesses the
desired performance attribute without effecting device performance.
2. Background
Some methods of radiopacifying a balloon catheter wherein the balloon
has an opacifying layer sandwiched between two other polymeric layers have
been described. In addition, coating of the internal lumen of a catheter
balloon
for radiopacity with the intent being to improve biocompatibility has been
attempted. In addition, some methods of compounding opacifyers directly into
the base material or chemically altering the polymer to accept a radiopaque
moiety into the molecule have been attempted. One problem with compounding
has been that the physical characteristics of the base material are often
times
changed due to the volume of opacifyier required to obtain proper radiopacity.
Another prior art method has included assembling precious metal bands onto
devices, such as catheters, in order to identify certain locations on the
catheter
shafts under fluoroscopy.
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Summary of Invention
The present disclosure relates to a coating comprising:
an acetoxy curable silicone binder comprising ceramic spheres ranging in size
from 5
microns to 50 microns, the ceramic spheres containing entrapped air; and
a polyvinylpyrrolidone agent blended with the acetoxy curable silicone binder,
wherein the
acetoxy curable silicone comprises recurring unit of the formula I:
(I)
CI I3 CH3 0
It
[Si¨Ojx ¨Si¨ (0¨('¨C113)2
CH3
wherein x is a positive integer.
The disclosure further relates to a medical device comprising:
an acetoxy curable silicone binder; and
a polyvinylpyrrolidone agent blended with the acetoxy curable silicone binder,
the acetoxy
curable silicone binder comprising sealed, air-filled ceramic microspheres
effective for enhancing a
return echo from the medical device to transducers in a 3D ultrasound system,
wherein the acetoxy
curable silicone comprises recurring unit of the formula I:
(I)
CH3 CH 0
It
[Si¨Oix¨Si¨(0¨C¨C113)2
C113
wherein x is a positive integer.
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3. Description
Although detailed embodiments of the invention are disclosed herein, it
is to be understood that the disclosed embodiments are merely exemplary of the
invention that may be embodied in various and alternative forms. Specific
structural and functional details disclosed herein are not to be interpreted
as
limiting, but merely as a basis for teaching one skilled in the art to
variously
employ the system embodiments.
Referred to herein are trade names for materials including, but not
limited to, polymers and optional components. The inventor herein does not
intend to be limited by materials described and referenced by a certain trade
name. Equivalent materials (e.g., those obtained from a different source under
a
different name or catalog (reference) number to those referenced by trade name
may be substituted and utilized in the methods described and claimed herein.
All
percentages and ratios are calculated by weight unless otherwise indicated.)
All
percentages are calculated based on the total composition unless otherwise
indicated. All component or composition concentrations are in reference to the
active level of that component or composition, and are exclusive of
impurities,
for example, residual solvents or by-products, which may be present in
commercially available sources.
Inventive subject matter described herein employs a Binder with an
appropriate opacifier formulated at a specific Wt%, and a solvent, if thinning
is
required, for application onto the device surface in one or repeated coats
until the
desired fluoroscopic opacity of the device is achieved. The opacifying coating
of
embodiments of the invention can be applied to the desired device surface by
spraying, sputtering, dipping, brushing, or by other means. Additionally, for
some embodiments, the Binder/opacifier can be applied to heat shrinkable
tubing
that can then be cut to length and reduced over a catheter shaft, providing a
lower cost alternative to using precious metal marker bands with equivalent
radiopacity.
Lubricious Coatings:
Lubricious coatings include members from a family of
Polyvinylpyrolodone (PVP), Polyvinylacetate (PVA), Cellulose Acetates,
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Paraylene, and others. All of these materials are hydrophilic surface coated
materials or in the case of paraylene, which is hydrophobic, used on catheter
shafts, guidewire shafts and balloons to provide lubricity to said devices
while
navigating them intravascularly. These coatings require only a single step or
a
two-step process; a base material is applied to receive a topcoat or
lubricious
coat on metal surfaces. These coatings are generally biocompatible. However,
there are hydrophobic materials that can provide both lubricity as well as
biocompatibility.
Embodiments of the invention allow for formulating a lubricious
material, as described above, directly into the Binder, which can then be
applied
to the desired device surface by spraying, sputtering, dipping, brushing, or
by
other means.
Eluting Agents:
A large body of work has been done in the prior art relating to the elution
of an agent or agents for functional or therapeutic reasons from the surface
of a
medical device. The majority of these agents are combined within hydrophilic
coatings; such as drugs or bio active agents. The drawback with hydrophilic
coatings is that the decay rates are rapid. There are several references to
impregnating polymeric materials with eluting agents within the prior art that
employ solvents and the eluting agents, which swell materials and flow into
the
polymer based on a concentration gradient, but not affect the molecular bonds
of
the substrate material. Once the material has been impregnated with the
desired
agent, the device is allowed to volatilize the solvent off wherein the eluting
agent
is trapped within the matrix of the medical device and will remain dormant
until
hydrolyzed within the body and allowed to elute at various rates, depending on
the base material.
Embodiments of the invention allow for mixing the eluting agent directly
into the Binder, where upon curing of the Binder, the agent elutes at a slower
more controlled rate due to the mechanical and physical properties of the
cured
Binder. Examples of this application include indicators on therapeutic devices
potentially coupled with antibiotics to retard bacterial growth, or
antibiotics
alone. One such example would be an antibiotic coating on a Foley catheter.
Other examples include, but are not limited to, drug coated PIC lines,
orthopedic
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set screws, shunts, and mesh used to repair tears or intra arterial disorders
by
incorporating bioactive materials or textured materials within the Binder
system.
Echogenic Properties:
Ultrasound is a widely accepted diagnostic method to evaluate soft tissue
organs, view developing Fetuses, and reconstruct images into 3D display
models. Unlike fluoroscopy, which uses lower energy X-ray radiation to
generate an image, Ultrasound utilizes sound waves of varying wavelengths and
the image is reconstructed based on the echo that is returned from the target
area.
It is the difference in tissue densities that enable Ultrasound to create an
image
based on the returning echo signature. The prior art cites several examples of
echogenic coatings which are coatings that, when applied, enable the coated
surface to be seen. In one embodiment described herein, an echogenic coating
used is formed by creating air pockets in a urethane coating to achieve a
density
difference whereby an image is generated. One issue with this method is lack
of
durability and compliance. Further, the process of deposing the coating is
burdensome and restricted to metal screws.
Embodiments of the invention utilize the Binder with ceramic spheres
that are in a range from 5 . - 50ji in diameter and contain entrapped air. It
is the
difference in densities between the ceramic sphere and the air that enables
the
echo to return to the collector in such a manner that an image is produced.
Thermal and Electrical Insulation:
There is less information relative to medical devices pertaining to
coatings that can provide electrical and thermal insulative properties.
Ceramic
depositions have been cited in the prior art for the coating of metal surfaces
requiring insulation, yet ceramic materials are non-compliant and may crack
whereby compromising electrical or thermal insulative properties. Also, the
cleanliness of the substrate surface is critical for proper insulative
adhesion when
e-beam or Vapor Deposition methods are employed to apply ceramic coatings to
the device surface.
Embodiments of the invention make insulating a desired material
substrate much easier by using the Binder material and ensures proper
electrical
or thermal insulative properties when applied by one of the methods cited
based
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on its physical properties. Additionally, the cured Binder material is
compliant,
yet well adhered to the substrate.
Chemical Indicators:
Chemical indicators are used to identify the presence of microbes or
chemical byproducts resulting in distinct color changes due to changes in PH,
or
other chemical changes. The indicators provide data relative to the presence
of
a particular molecule, acidity, agent, antigen, antibody and the like. Such
indicators are primarily incorporated into a substrate and are not the result
of a
coating. The prior art has limited information relative to the use of an
indicator
for the presence of various forms of bacteria on the surface of medical
devices
such as, but not limited to, PIC Line catheters, Colostomy tubes, Introducers,
and the like.
Embodiments of the invention address this need by combining the
appropriate indicator with the Binder at the required Wt% and using an
appropriate solvent to thin the formulation for application. Further, the
chemical
indicators could be integrated within the Binder as described above and coated
onto an appropriate substrate for placement within open or sealed portions of
fresh meat such as beef, fowl, muscles, and fish. If bacteria were present,
the
package indicator would change colors thereby identifying a bacterial colony
which could then be cultured and identified and dealt with prior to consumer
contact.
The chemical indicator could also be used for screening for a variety of
rather virulent diseases found or passed on in foodstuffs. In addition, each
food
group could be monitored for the incidence of bacterial contamination prior to
reaching the consumer market.
4. Summary
Embodiments of the invention relate to a versatile system wherein the
active agent can be incorporated into a base Binder and applied by methods
including, yet not limited to, dipping, spraying, fogging in a chamber,
brushing
and the like, depending on the geometry of the device.
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In addition, curing mechanisms of the Binder may include, but are not
limited to, U.V.& RTV curable materials, thermal, chemical and room
temperature cures.
The Binder Material Utilized Within Embodiments of the Invention:
In one embodiment, the Binder material includes a Room Temperature
Vulcanization (RTV) silicone elastomer solubilized within an appropriate
solvent at a weight percentage of between 1% and 65%, which cures via
extraction of moisture from the atmosphere wherein the polymer utilizes the
hydroxyl group (OH) from a water molecule to initiate and complete cross
linking of the silane monomer. See Figures 1 and 2 below for an example of the
curing mechanism.
CH3 CH3 0
I I II
...l - Si ¨ Olx ¨ (Si ¨ (0 ¨ C ¨ CH3)2
I * Diacetoxy group/
Copolymer
CH3 I
Sily1 End
Figure 1
CH3 CH3 0 CH3 0
I I I I I II
...[Si-Olx-Si (0-C-CH3)2 + H20> ...[Si-Olx- Si-OH + HO-C - CH
I I I Acetic Acid
CH3 CH3 o
I
Dimethylsiloxane C = 0
1
CH3
Figure 2 Hydroxy Ligand
The curing mechanism includes an acetoxy system in which the chain
contains a dimethysiloxane along with a copolymer. See Figure 1 above. The
copolymer contained on the dimethylsiloxane chain contains a
methyldiacetoxysilyl group. Curing is achieved by exposure of the elastomer to
air. Water particles, or hydroxyl groups (Off), from moisture in the air react
to
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form acetoxy ligans which in turn form free radicals comprised of acidic acid
and hydroxy ligands.
It is these acetoxy ligands, which react with other acetoxy ligans on other
branches to form Si-O-Si cross-links between polymer chains, with the
liberation
of acidic acid. A catalyst can be added in order to accelerate the process yet
not
effect the final outcome. See Figure 2 above.
In one example illustrating the utility of one embodiment of the present
invention, a catheter may be equipped with a compliant expandable balloon.
Using one embodiment of the invention, the balloon may be coated on the
exterior with a compliant radiopacifying agent, wherein said radiopacifying
agent can be Bismuth bicarbonate, Barium Sulfate, Tungsten, Tantalum, Iodides,
Borates or other such radiopacifying agents. In one embodiment, the catheter
balloon is coated with a radiopacifying agent comprising the (W) or Tungsten
radiopacifying agent combined with a Binder, wherein said Binder is a silicone
dispersion. In combination with the radiopacifying agent, the Binder material
used, such as a polydimethyl siloxane, can be dispersed in an appropriate
solvent
such as aliphatic hydrocarbons, butylacetate, ethylacetate or THF, all of
which
are capable of solubilizing elastomeric and polymeric Binder's from a variety
of
materials such as Silicones, Urethanes, Nitryles, Amides and other polymeric
materials which can be dispersed within a solvent and be used as the Binder
Agent. These materials, when compounded with a radiopacifying agent can be
used to coat a medical device for radiopacity. The materials cited in this
example
are not exclusively limited to the design, yet are viable to its development.
Citing another example, said (Acetoxy curable silicone Binder material)
including a polydimethylsiloxane into which a radiopacifying or other desired
agent is combined in an approximate range from 1 Wt% to 60 Wt%. The active
agent is suspended within the polydimethylsiloxane, subsequently thinned for
application and applied to a guidewire tip, catheter tip, heat shrinkable
tubing
and the like by methods not limited to dipping, brushing, and spraying, or
other
such methods. The coating may be applied once or multiple times to achieve the
desired performance characteristics. Furthermore, the coating may be applied
to
medical devices whole or in part, based on the desired characteristics.
Portions
of the medical device surface may be masked in order to selectively coat the
device surface. Further, a sealing agent including a Binder such as
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polydimethylsiloxane with no active ingredient(s) can be applied to surfaces
that
will encapsulate the desired agent and aid in biocompatibility. This topcoat
may
consist of the Binder material without any active ingredients except for the
desired solvent to achieve the correct Wt.% ratio of solvent to filler.
The disclosed coating system, once cured, is compliant and capable of
adhering to the mechanical requirements of a particular device. A surface
primer
may also be employed to pre-condition a balloon or other device surface to
accept the Binder material and appropriate constituent. Such primers would
come from a family of acrylates, urethanes, hydrolytes and amides and the
like.
In addition to the radiopacifying capability of this embodiment,
additional functional materials may be added to the Binder material(s) in
order to
provide other desired characteristics to a medical device such as lubricity,
elution of a desired compound such as a drug, or the use of a chemical
indicator
for the detection of organisms such as bacteria, bio active agents, or thermal
or
electrical insulators..
As an example: The versatility of embodiments of the invention allow for
at least a permanently enhanced device which retains its intended physical
characteristics yet provides a useful enhancement such as utilizing a chemical
indicator for the detection of unwanted microbes on the surface of various
medical devices which are percutainously placed and remain indwelling for a
terminal period of time.
In this example, a gram positive stain could be formulated with the
Binder to form a coating which in the presence of bacteria such as
Staphylococcus, Streptoccus, Clostridium, Bacillus and Lysteria the coating
would change color from clear to purple indicating the presence of a bacterial
colony reactive with Gram Stain. With said color change, the device can be
removed from the patient and a new device placed.
Active Agents:
Within embodiments of the present invention, the Active Agents that are
added to the Binder provide the unique characteristic to be achieved on a
medical device. Examples include, but are not limited to, radiopacification,
lubricity, echogenicity, insulative properties, therapeutic coating, pigments,
chemical indicators, and bioactive agents. The agents are formulated into the
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Binder on a Wt% basis and are mechanically suspended within the matrix of the
Binder once the Binder has cured. By design, there is no chemical interaction
taking place between the Binder and the Active Agents because chemically
altering the active agent could compromise its performance. Once the Binder
cures, the Active Agents added to the Binder are encapsulated within the
Binder
matrix unless the Active Agent is miscible in water, in which case, being
porous,
the Binder will allow for slow elution of the Active Agent. The speed of
elution
depends on the concentration or Wt% of Active Agent loaded into the Binder
that determines the concentration gradient between the surrounding fluid
filled
interstitial space and the device coating itself.
Additional Embodiments:
The base Binder as described herein and the active ingredients can be
applied to a variety if medical grade materials in order to produce a robust
low
cost means of providing unique performance characteristics to a variety of
medical devices. As an example, most current marker bands are made from
costly precious metals such as platinum, gold. These metals provide excellent
differentiation under fluoroscopy, but increases device costs considerably.
Embodiments of the invention enable the user to enjoy the benefits of
radiopacity at a lower cost and with comparable resolution by combining an
opacifier to the binder to provide proper visualization under flouroscopy.
In yet another embodiment, the coating would utilize an air filled
microsphere embedded within the Binder in order to provide a coating capable
of allowing medical devices to be visualized under Ultrasound. The reason for
sealed air-filled microspheres would be to enhance the return echo from the
coated device to the multiple transducers utilized in a 3D ultrasound system.
In
addition, a non-ferrous material may be used within the Binder to coat the
balloons or other devices in lieu of ferrous material, for applications in
diagnostic instruments such as MRI or CT scanners. Conversely, a magnetic
material consisting of the ferrous materials ranging from basic magnetic
materials to the more exotic rare earth magnetic materials such as "neodymium
iron boron" and the like can be utilized within the Binder system disclosed
earlier within this document.
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Since the invention disclosed herein may be embodied in other specific
forms without departing from the spirit or general characteristics thereof,
some
of which forms have been indicated, the embodiments described herein are to be
considered in all respects illustrative and not restrictive. The scope of the
invention is to be indicated by the appended claims, rather than by the
foregoing
description, and all changes, which come within the meaning and range of
equivalency of the claims, are intended to be embraced therein.
